Conjugate gaze palsies are

neurological Neurology (from el, νεῦρον (neûron), "string, nerve" and the suffix -logia, "study of") is the branch of medicine dealing with the diagnosis and treatment of all categories of conditions and disease involving the brain, the spinal ...

disorder Disorder may refer to randomness, non-order, or no intelligible pattern. Disorder may also refer to: Healthcare * Disorder (medicine), a functional abnormality or disturbance * Mental disorder or psychological disorder, a psychological pattern a ...

s affecting the ability to move both eyes in the same direction. These palsies can affect

gaze In critical theory, sociology, and psychoanalysis, the gaze (French ''le regard''), in the philosophical and figurative sense, is an individual's (or a group's) awareness and perception of other individuals, other groups, or oneself. The concept ...

in a horizontal, upward, or downward direction. These entities overlap with ophthalmoparesis and ophthalmoplegia.

Signs and symptoms

Symptoms of conjugate gaze palsies include the impairment of gaze in various directions and different types of movement, depending on the type of gaze palsy. Signs of a person with a gaze palsy may be frequent movement of the head instead of the eyes. For example, a person with a horizontal saccadic palsy may jerk their head around while watching a movie or high action event instead of keeping their head steady and moving their eyes, which usually goes unnoticed. Someone with a nonselective horizontal gaze palsy may slowly rotate their head back and forth while reading a book instead of slowly scanning their eyes across the page.

Cause

A lesion, which is an abnormality in tissue due to injury or disease, can disrupt the transmission of signals from the brain to the eye. Almost all conjugate

palsies originate from a lesion somewhere in the

brain stem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is conti ...

, usually the

midbrain The midbrain or mesencephalon is the forward-most portion of the brainstem and is associated with vision, hearing, motor control, sleep and wakefulness, arousal (alertness), and temperature regulation. The name comes from the Greek ''mesos'', " ...

, or

pons The pons (from Latin , "bridge") is part of the brainstem that in humans and other bipeds lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum. The pons is also called the pons Varolii ("bridge of Va ...

. These lesions can be caused by

stroke A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...

, or conditions such as Koerber-Salus-Elschnig syndrome,

Progressive supranuclear palsy Progressive supranuclear palsy (PSP) is a late-onset degenerative disease involving the gradual deterioration and death of specific volumes of the brain. The condition leads to symptoms including loss of balance, slowing of movement, difficulty ...

, Olivopontocerebellar syndrome, Niemann-Pick Disease, Type C, or envenomation such as from a scorpion sting.

Mechanism

The location of the lesion determines the type of palsy. Nonselective horizontal gaze palsies are caused by lesions in the

Abducens nucleus The abducens nucleus is the originating nucleus from which the abducens nerve (VI) emerges—a cranial nerve nucleus. This nucleus is located beneath the fourth ventricle in the Anatomical terms of location, caudal portion of the pons, Anatomical t ...

. This is where the cranial nerve VI leaves on its way to the

Lateral rectus muscle Lateral is a geometric term of location which may refer to: Healthcare *Lateral (anatomy), an anatomical direction *Lateral cricoarytenoid muscle *Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics *Lateral cons ...

, which controls eye movement horizontally away from the midline of the body. The cranial nerve VI also has

interneuron Interneurons (also called internuncial neurons, relay neurons, association neurons, connector neurons, intermediate neurons or local circuit neurons) are neurons that connect two brain regions, i.e. not direct motor neurons or sensory neurons. I ...

s connecting to the

medial rectus The medial rectus muscle is a muscle in the orbit near the eye. It is one of the extraocular muscles. It originates from the common tendinous ring, and inserts into the anteromedial surface of the eye. It is supplied by the inferior division of ...

, which controls horizontal eye movement towards from the midline of the body. Since the lateral rectus controls movement away from the center of the body, a lesion in the abducens nucleus disrupts the pathways controlling outward movements, not allowing the right eye to move right and the left eye to move left. Nerve VI has the longest subarachnoid distance to its target tissue, making it susceptible to lesions. Lesions anywhere in the abducens nucleus, cranial nerve VI neurons, or interneurons can affect eye movement towards the side of the lesion. Lesions on both sides of the abducens nucleus can cause a total loss of horizontal eye movement. One other type of gaze palsy is a horizontal saccadic palsy.

Saccades A saccade ( , French for ''jerk'') is a quick, simultaneous movement of both eyes Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling s ...

are very quick intermittent eye movements. The

paramedian pontine reticular formation The paramedian pontine reticular formation, also known as PPRF or paraabducens nucleus, is part of the pontine reticular formation, a brain region without clearly defined borders in the center of the pons. It is involved in the coordination of eye ...

(PPRF), also in the pons is responsible for saccadic movement, relaying signals to the abducens nucleus. Lesions in the PPRF cause what would be saccadic horizontal eye movements to be much slower or in the case of very severe lesions, nonexistent. Horizontal gaze palsies are known to be linked to Progressive

Scoliosis Scoliosis is a condition in which a person's spine has a sideways curve. The curve is usually "S"- or "C"-shaped over three dimensions. In some, the degree of curve is stable, while in others, it increases over time. Mild scoliosis does not t ...

. This occurs because pathways controlling saccadic movements are disrupted by the lesion and only slow movements controlled by a different motor pathway are unaffected. Lesions in the midbrain can interfere with efferent motor signals before they arrive at the pons. This can also cause slowed horizontal saccadic movements and failure for the eye to reach its target location during saccades. This damage normally happens in the

oculomotor nucleus The fibers of the oculomotor nerve arise from a nucleus in the midbrain, which lies in the gray substance of the floor of the cerebral aqueduct and extends in front of the aqueduct for a short distance into the floor of the third ventricle. From t ...

of the midbrain As in horizontal saccadic palsy, the saccades are stopped or slowed from the disrupted pathway, only in this case the signal is disrupted before it reaches the PPRF. One-and-a-half syndrome is associated with damage to the

and the

medial longitudinal fasciculus The medial longitudinal fasciculus (MLF) is an area of crossed over tracts, on each side of the brainstem. These bundles of axons are situated near the midline of the brainstem. They are made up of both ascending and descending fibers that ari ...

. These combined damages cause both a complete gaze impairment on the ipsilateral side and a "half" gaze impairment on the contralateral side. As seen in horizontal saccadic palsy, the impairment of the contralateral side gaze is caused by the disrupted pathways coming from the PPRF, while the "half" impairment is from the signal passing through the medial longitudinal fascicles not being able to reach its target. One-and-a-Half syndrome is normally associated with horizontal gaze. Although more rare than horizontal, one-and-a-half syndrome from damage to the paramedian pontine reticular formation and the medial longitudinal fasciculus can be shown to affect vertical gaze. This can cause impairment of vertical gaze, allowing only one eye to move vertically.

Diagnosis

A patient may be diagnosed with a conjugate gaze palsy by a physician performing a number of tests to examine the patient's eye movement abilities. In most cases, the gaze palsy can simply be seen by inability to move both eyes in one direction. However, sometimes a patient exhibits an abduction

nystagmus Nystagmus is a condition of involuntary (or voluntary, in some cases) eye movement. Infants can be born with it but more commonly acquire it in infancy or later in life. In many cases it may result in reduced or limited vision. Due to the invol ...

in both eyes, indicating evidence of a conjugate gaze palsy. A nystagmus is a back and forth "jerk" of the eye when attempting to hold a gaze in one direction.

Classification

Conjugate gaze palsies can be classified into palsies affecting horizontal gaze and vertical gaze.

Horizontal gaze palsies

Horizontal gaze palsies affect gaze of both eyes either toward or away from the midline of the body. Horizontal gaze palsies are generally caused by a lesion in the brain stem and connecting nerves, normally in the

Progressive scoliosis

Horizontal gaze palsy with progressive scoliosis (HGPPS) is a very rare form of conjugate gaze palsy, appearing only in a few dozen families worldwide. HGPPS prevents horizontal movement of both eyes, causing people with this condition to have to move their head to see moving objects. In addition to the eye movement impairment, HGPPS is coupled with progressive scoliosis, although eye symptoms usually appear before scoliosis. HGPPS is caused by a mutation in the ROBO3 gene, which is important in cross-over of motor and sensory signals, preventing horizontal eye movement. In addition to the mutation, lesions in the midbrain and pons are common. This can also include a complete absence of a formation in the pons, the

facial colliculus The facial colliculus is an elevated area located in the pontine tegmentum (dorsal pons), within the floor of the fourth ventricle (i.e. the rhomboid fossa). It is formed by fibres from the facial motor nucleus looping over the abducens nucleus. T ...

, which is responsible for some facial movements. The cause of progressive scoliosisin HGPPS and why HGPPS does not affect vertical gaze is unclear. Progressive scoliosis is normally treated with surgery.

Vertical gaze palsies

Vertical gaze palsies affect movement of one or both eyes either in upward direction, up and down direction, or more rarely only downward direction. Very rarely only movement of one eye in one direction is affected, although by definition this is not a conjugate gaze palsy, because by definition conjugate gaze palsies affect movement of both eyes. Vertical gaze palsies are often caused by lesions to the midbrain due to a stroke or a tumor. In the case that only downward gaze is affected, the cause is normally progressive supranuclear palsy.

Treatment

There is no treatment of conjugate gaze palsy itself, so the disease or condition causing the gaze palsy must be treated, likely by surgery. As stated in the causes section, the gaze palsy may be due to a lesion caused by stroke or a condition. Some of the conditions such as Progressive supra nuclear palsy are not curable, and treatment only includes therapy to regain some tasks, not including gaze control. Other conditions such as Niemann-Pick disease type C have limited drug therapeutic options. Stroke victims with conjugate gaze palsies may be treated with intravenous therapy if the patent presents early enough, or with a surgical procedure for other cases.

Prognosis

The prognosis of a lesion in the visual neural pathways that causes a conjugate gaze palsy varies greatly. Depending on the nature of the lesion, recovery may happen rapidly or recovery may never progress. For example,

optic neuritis Optic neuritis describes any condition that causes inflammation of the optic nerve; it may be associated with demyelinating diseases, or infectious or inflammatory processes. It is also known as optic papillitis (when the head of the optic nerv ...

, which is caused by inflammation, may heal in just weeks, while patients with an

ischemic optic neuropathy Ischemic optic neuropathy (ION) is the loss of structure and function of a portion of the optic nerve due to obstruction of blood flow to the nerve (i.e. ischemia). Ischemic forms of optic neuropathy are typically classified as either anterior is ...

may never recover.National Stroke Association. Stroke Treatment.

References

External links

{{Medical resources , DiseasesDB = 19291 , ICD10 = H51.0 , ICD9 = {{ICD9, 378.81 , ICDO = , OMIM = , MedlinePlus = , eMedicineSubj = , eMedicineTopic = , MeshID = , GeneReviewsNBK = , GeneReviewsName = Eye diseases Neurological disorders Visual disturbances and blindness